In LTE/LTE-Advanced, MIMO techniques are adopted for enhancing system capacity, cell-edge user throughput and the like. Also, a heterogeneous network technique is adopted for realizing high quality communication by reducing inter-cell interference while different types of base stations (macro cell, small cell and the like) coexist.
Especially, in a small cell of the heterogeneous network, it is assumed to use a high frequency band. Here, since propagation loss increases in the high frequency band, in order to compensate it, it is considered to apply massive MIMO that performs narrow beamforming in which the beam width is narrow.
The massive MIMO is a large-scale MIMO having many antennas (example: 100 elements) in the base station side, by which inter-user interference can be made small since the strength of the electric field can be concentrated on a small area.